Low intensity radiant infrared heating systems of the type described above are preferred over forced air and hot water systems, for example, in many applications. This preference is due in large part to the fact that radiant heating involves direct energy conversion in the sense that persons, plants and animals in the heated areas receive sensible heat via direct energy absorption in their own tissue rather than through the movement of air which has been heated. As a result, people can work comfortably in areas where the actual air temperature is lower than that required for comfort in forced air and convection systems; this, of course, gives rise to substantial energy savings. In addition, a concrete floor under an infrared emitter will absorb energy in the range of frequencies characteristic of radiant tube systems and will thereafter release thermal energy through reradiation to make the enclosure more comfortable and healthful for its inhabitants on an economical basis. Such reradiation from the floor warms the feet of persons working or living in the affected area not only during heating system operation but afterwards as well. Infrared systems have the further advantage in greenhouses and the like of positively affecting plant growth rates.
Low intensity infrared systems have the further advantages of high directionality through the use of reflectors which aim the radiation where it is needed, thus increasing effective utilization.
A low intensity radiant energy heating system of the type previously described is typically installed with the emitter tube 7 to 50 feet above floor level. Reflectors in the form of thin metal fabrications or stampings are installed immediately above the emitter tube over substantially the entire operating length thereof to direct the emitted radiation toward the floor. Due to natural convection between emitter surface and reflector, these thin reflectors become hot and transfer energy from the system to the upper areas, ceiling and roof of the enclosure primarily through two mechanisms: convection currents caused by temperature differences and disturbances within the enclosure actually scrub heat off of the top and sides of the reflector and allow it to move toward the ceiling where it is wasted; in addition, the reflector itself becomes hot enough to reradiate energy from the outside surfaces thereof and this radiation is directed away from rather than toward the area where heating effect is best utilized. Since the reflector of a typical installation provides a large area for heat loss, it becomes a primary factor in low utilization of radiant energy.